We are requesting funds to purchase a JEM 1200EX transmission electron microscope, to be used by cell biologists and neuroscientists who require high resolution in structural studies. The microscope will be used by investigators in both basic science and clinical departments, in keeping with a long-standing tradition of interdepartmental and interdisciplinary collaboration at Case Western Reserve University. The need for a new microscope has been caused by both the addition of new faculty members and the deterioration of out-moded equipment. The microscope is essential to several investigators of structure and function in the nervous system, including studies of the blood- brain barrier, of astrocytes, and of developing and mature synapses. The resolution provided by this state-of-the-art instrument is important to analyses of rapidly-frozen, freeze- fractured tissue, of immunocytochemical preparations, and in studies requiring serial thin-section reconstruction. The capabilities of the new instrument, in concert with experimental design and selected methods, will allow us to examine structure with a resolution which permits inference about molecular composition.